Cytotoxic T lymphocytes (CTL) are likely to play an important role in limiting the spread of the human immunodeficiency virus (HIV) in infected individuals. This cellular immune response will be studied in simian immunodeficiency virus (SIV)-infected rhesus monkeys. In these studies we will assess: I. SIV CTL epitopes and restricting MHC class I molecules in rhesus monkeys. II. T cell receptor V gene usage in SIV-infected monkeys. III. The role of CTL pressure in the selection of SIV mutations. IV. Novel vaccine approaches for the generation of SIV-specific CTL. V. The contribution of CTL in the control SIV spread during primary infection.